The present invention is generally related to optical networks and, more particularly, to signal traffic protection in linear optical networks.
Optical networks conventionally compensate for deleterious linear effects to maintain the integrity of signals sent over the optical fibers of the network. To protect the integrity of signal traffic carried on the operative link carrying the signals against interruption or failure, e.g., a line cut, protection optical fibers are invoked. The signal traffic is switched from an interrupted working optical fiber to a protection optical fiber. In many arrangements the operative link reverts back to the working optical fiber once it is repaired.
In a link having 1+1 protection, the link has at least four optical fibers, one pair (working and protection) for carrying optical signals in one direction and a second pair (working and protection) for carrying optical signals in the opposite direction. The transmitting node sends the network optical signals on both the working optical fiber and a protection optical fiber. The receiving node accepts the optical signals on the working optical fiber but switches to the protection optical fiber upon detection of a fault in the working optical fiber.
Conventionally protection arrangements such as described use a protection switching protocol after the conversion of the optical signals into electrical signals. This protection switching protocol is performed in the upper layers of the optical network architecture. For example, many optical networks use SONET/SDH (Synchronous Optical NETwork/Synchronous Digital Hierarchy) protocol. This protocol operates above the physical layer, the lowest layer defined in the often-taught OSI (Open Systems Interconnection) model. Such networks often use the high level SONET/SDH protocol in the network's protection system, typically a 1+1 protection system.
Such high level protocols for the two nodes of a link require relatively complex information exchanges between the two nodes. It is desirable that the requirements of such protection be simplified.